Device and method for treating central nervous system pathology

ABSTRACT

The present invention relates generally to a device and method for treating tissues of the central nervous system and more particularly, but not exclusively, to a device and method for treating the brain tissue.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 12/351,331, filed Jan. 9, 2009, now U.S. Pat. No. 8,267,960, which claims the benefit of priority of U.S. Provisional Application 61/019,968, filed on Jan. 9, 2008, and U.S. Provisional Application No. 61/081,997, filed on Jul. 18, 2008, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to a device and method for treating tissues of the central nervous system using sub-atmospheric pressure and more particularly, but not exclusively, to a device and method for treating the brain tissue using sub-atmospheric pressure.

BACKGROUND OF THE INVENTION

The anatomy, physiology, and pathologic processes that involve the central nervous system (CNS) make CNS tissue unique. The preservation of both the three-dimensional structural anatomy and the microanatomical relationships of neurons (whose function depends specifically on spatial relationships with other neurons and other supporting cells), as well as the maintenance of properly oxygenated blood flow and the homogeneous ground substance matrix in which the neurons survive, are vital to the survival and function of the central nervous system tissues. Moreover, the inability of central nervous system cells to regenerate emphasizes the need to maximize survival of every possible neuron. For reasons such as these, treatment of both open and closed space pathology in the central nervous system is unique.

Among the clinical problems that threaten survival of CNS tissues, the control of central nervous system edema, infection, and blood supply are central. The brain responds to trauma and injury by collecting a significant amount of interstitial edema. Because the brain is enclosed in a closed space (the dura and skull), edema results in compression and compromise of the blood flood and nutritional performance of the CNS, which greatly impairs physiological recovery of the central nervous system and often of itself results in progression of compromise and death of the CNS parenchyma. Currently available treatments for reducing edema include agents to decrease vascular permeability (glucocorticoids: Dexamethasone, Prednisone, Methyl Prednisolone), diuretics, mechanical ventricular drainage, resection of the brain parenchyma, and extensive craniectomy. However, disadvantages to these treatments include poor results, complications from the drugs, and inconsistent results.

The need for rapid and effective treatment is also vital due to the disastrous consequences and high likelihood of rapid propagation of infection and edema in the CNS. At present there are few successful methods available to treat pathologies affecting the intracranial and intraspinal space, CNS parenchyma, and the surrounding structures. Where elsewhere tissues can be treated with dressing changes, the CNS is not amenable to this type of treatment because of its inaccessibility, precarious structure, propensity for infection, and progression of injury. There is evidence that inflammation and immunological response to central nervous system trauma and other pathology are of equal or greater long term consequences than the initial trauma or insult. The response of the CNS to decreased blood flow secondary to edema results in hypoxia and ischemia/reperfusion-mediated injury. These injuries contribute to the neuropathological sequella, which greatly contribute to the adverse outcome of head injury.

In addition, the brain requires a continuous supply of oxygenated blood to function and survive. Within three minutes of complete interruption of blood flow to the brain, irreversible brain damage results, though the brain can however remain viable and recover from reduced blood flow for more prolonged periods. There is evidence that focal areas of the brain can remain ischemic and relatively functionless for days and still recover. This finding has led to the concept of an ischemic zone, termed the penumbra or halo zone, that surrounds an area of irreversible injury. A secondary phenomena is the release of excitotoxins that are released locally by injured neurons, alterations in focal blood flow, and edema.

Cerebrovascular disease may be a result of: inadequate blood flow to the brain cells from decreased perfusion pressure, rupture of a blood vessel resulting in direct injury to the local brain area and by compression of adjacent tissue. Intrinsic disease of the brain blood vessels such as atherosclerosis, aneurysm, inflammation, etc. or a remote thrombus that lodges in the brain blood vessels from elsewhere such as the heart can produce cerebrovascular disease. A stroke is a term that defines a neurological injury that occurs as a result of some of these pathologic processes. Five percent of the population over 65 are affected by cerebrovascular diseases which are the third leading cause of death in the developed world. In addition, lifelong debility, inability to work and function in society and the family, and the frequent need for nursing home treatment often result. People affected by strokes usually have significant impairments for the rest of their lives.

A stroke in evolution, or progressive stroke, refers to a neurological deficit that progresses or fluctuates after the initial event. It is thought that this occurs because of progressive spasm or narrowing of the involved artery, development of cerebral edema around the initial injury, thrombus propagation as a result of decreased blood flow or release of local cytokines from injured brain cells. Fortunately there are some communications between vessels in the brain called collateral circulation. Supplying blood from these collateral vessels may prevent death of brain cells in the ischemic zone.

In cases of intracranial hemorrhage, the hemorrhage usually begins as a small mass that grows in volume by pressure dissection and results in displacement and compression of adjacent brain tissue. Edema in the adjacent compressed tissue around the hemorrhage may lead to a mass effect and a worsening of the clinical condition by damaging a larger area of brain tissue. Edema in the adjacent brain may cause progressive deterioration usually seen over 12 to 72 hours. The occurrence of edema in the week following the intracerebral hemorrhage often worsens the prognosis, particularly in the elderly. The tissue surrounding the hematoma is displaced and compressed but is not necessarily fatally compromised. Improvement can result as the hematoma is resorbed and the involved tissue regains function.

Treatment of these conditions has been disappointing. Surgical decompression of hemorrhage can be helpful in some cases to prevent irreversible compression. Agents such as mannitol and some other osmotic agents can reduce intracranial pressure caused by edema. Steroids are of uncertain value in these cases, and recently hyperbaric oxygen has been proposed.

Thus, though the application negative (or sub-atmospheric) pressure therapy to wounded cutaneous and subcutaneous tissue demonstrates an increased rate of healing compared to traditional methods (as set forth in U.S. Pat. Nos. 5,645,081 and 5,636,643, 7,198,046, and 7,216,651 as well as US Published Application Nos. 2003/0225347, 2004/0039391, and 2004/0122434, the contents of which are incorporated herein by reference), there remains a need for devices and methods specifically suited for use with the unique tissues of the central nervous system.

SUMMARY OF THE INVENTION

The present invention relates generally to a device and method for treating tissues of the central nervous system using sub-atmospheric pressure and more particularly, but not exclusively, to a device and method for treating brain tissue using sub-atmospheric pressure. According to one exemplary procedure the present invention provides a method for treating damaged central nervous system tissue using sub-atmospheric pressure comprising locating a porous material proximate the damaged central nervous system tissue to provide gaseous communication between one or more pores of the porous material and the damaged central nervous system tissue. In some cases the porous material may be located directly over the damaged central nervous system tissue. The porous material may be sealed in situ proximate the damaged central nervous system tissue to provide a region about the damaged central nervous system tissue for maintaining sub-atmospheric pressure at the damaged central nervous system tissue. A vacuum system may then be operably connected with the porous material and the vacuum system activated to provide sub-atmospheric pressure at the damaged central nervous system tissue. The sub-atmospheric pressure may be maintained at the damaged tissue for a time sufficient to decrease edema at the central nervous system.

In another of its aspects the present invention provides an apparatus for treating damaged central nervous system tissue. The apparatus may include a porous bioabsorbable material, such as an open-cell collagen, having pore structure configured to permit gaseous communication between one or more pores of the porous material and the central nervous system tissue to be treated. The bioabsorbable nature of the porous material can obviate the need for a second procedure to remove the porous material. The apparatus also includes a vacuum source for producing sub-atmospheric pressure; the vacuum source may be disposed in gaseous communication with the porous material for distributing the sub-atmospheric pressure to the central nervous system tissue. The porous material may have, at least at a selected surface of the porous material, pores sufficiently small to prevent the growth of tissue therein. In addition, the porous material may have, at least at a selected surface of the porous material, a pore size smaller than the size of fibroblasts and central nervous system cells, and may have a pore size at a location other than the selected surface that is larger than that of fibroblasts and central nervous system cells. The pore size of the porous material may be large enough to allow movement of proteins the size of albumin therethrough. Also, the porous bioabsorbable material may include at least one surface that is sealed to prevent the transmission of sub-atmospheric pressure therethrough. The apparatus may also include a cover configured to cover the damaged central nervous system tissue to maintain sub-atmospheric pressure under the cover at the damaged central nervous system tissue.

In use, the present invention can provide a pressure gradient to remove edema from the central nervous system, thus preserving neurologic function and increasing the probability of recovery and survival in a more physiologically preserved state. Decrease in central nervous system edema in turn can lead to a decrease in intracranial pressure, minimizing the risk of central nervous system compromise and herniation. In addition to the removal of edema, the present invention can remove mediators, degradation products, and toxins that enhance the inflammatory and neuropathological response of tissues in the central nervous system to injury.

The present invention can protect the central nervous system from exogenous infection and contamination, and facilitates and maximizes healing of the intracranial and adjacent structures when tissues are contaminated by central nervous system abscesses, meningitis, ventriculitis, and brain tissue infection. The central nervous system tissue may also be protected from adjacent infection, such as infection which exists subclinically in the sinuses, oral cavity, and other potentially infected spaces that exist in the normal human state, either by increased blood flow and directly decreasing bacterial load. Moreover, the device and method of the present invention can prepare central nervous system tissue to achieve a stage of healing and diminution of bacterial counts such that acceptance of secondary treatments (e.g., flaps, bone grafts) can be successful.

The present invention can also facilitate closure of pathologic openings communicating between the central nervous system and the extradural space, e.g. between the extradural space and the subdural/epidural, and/or subarachnoid space. Likewise, the progression of pathologic processes, disruption of physiological central nervous system integrity, the interference with central nervous system blood flow and nutrition can be minimized.

The devices and methods of the present invention can be used to treat the following conditions: exposure of the central nervous system as a result of trauma, surgery, infection, or any other pathologic process; treatment of any of the spaces and tissues surrounding the central nervous system, including the subdural/epidural and intraventricular spaces; treatment of edema of the central nervous system parenchyma secondary to any cause, including hemorrhage, trauma, tumor, infection or any other pathologic state; treatment of elevated intracranial and intraspinal pressure due to the any of the aforementioned causes; and treatment of cerebrospinal fluid pathology in which the spinal fluid is pathologically in communication with any non-anatomical and non-physiologic spaces. In addition, the present invention can be used to promote formation of granulation tissue in areas where central nervous system disruption has occurred, and to control cerebrospinal fluid leaks. Further, the modified present material can be used for control or closure of defects existing between the central nervous system, the cutaneous space, intranasal space, and intrasinus space.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary and the following detailed description of the preferred embodiments of the present invention will be best understood when read in conjunction with the appended drawings, in which:

FIG. 1 schematically illustrates a perspective view in partial cross-section of an exemplary apparatus of the present invention in situ showing treatment of an injury to the brain;

FIGS. 2 and 3 illustrate MRI scans of control animals having brain injuries that were not treated with sub-atmospheric pressure;

FIG. 4 illustrates an MRI scan of an animal having a brain injury that was treated for 8 hours with sub-atmospheric pressure;

FIG. 5 illustrates an MRI scan of a control animal having a brain injury that was not treated with sub-atmospheric pressure;

FIGS. 6 and 7 illustrate MRI scans of animals having brain injuries that were treated for 24 hours with sub-atmospheric pressure;

FIG. 8 illustrates an MRI scan of a control animal having a brain injury that was not treated with sub-atmospheric pressure;

FIG. 9 schematically illustrates in partial cross-section the normal anatomy of the rat skull including the brain and surrounding muscle, bone, and other tissues;

FIG. 10 schematically illustrates in partial cross-section slice 12/26 of the animal of FIG. 2, showing the area of impaction and accumulation of blood or fluid;

FIG. 11 schematically illustrates in partial cross-section slice 12/24 of the animal of FIG. 4, showing the area of impaction with porous material and drape in place;

FIG. 12 schematically illustrates in partial cross-section slice 12/24 of the animal of FIG. 5, showing the area of impaction with porous material in place;

FIG. 13 schematically illustrates in partial cross-section slice 12/24 of the animal of FIG. 6, showing the area of impaction with porous material and drape in place;

FIG. 14 schematically illustrates a multi-layer porous material of the present invention;

FIGS. 15A and 15B illustrate the lower right panel of the MRI scan of FIGS. 5 and 6, respectively, enlarged to show the relatively greater fluid content in the impacted brain of the non-treated animal;

FIG. 16 illustrates T2-weighted MR images from axial planes illustrating the localization of MR spectra voxels acquired from rat brain in vivo;

FIG. 17 illustrates single-voxel MR spectra obtained from brains of sham surgery, brain injured and brain injured plus treatment. The metabolites are labeled as Ins (myoinositol), Tau (taurine), Cho (choline-containing compounds), Cr+PCr (creatine and phosphorus creatine), Glu+Gln (glutamate and glutamine), NAA (N-acetyl aspartate), GABA (γ-aminobutyric acid) and Lac (lactate); and

FIGS. 18A and 18B illustrate immunohistochemical analysis of neuronal degradation and death performed by staining for nitrotyrosine on brain samples harvested 72 hours after impaction with the treated group exposed to sub-atmospheric pressure for the entire 72 hours; dark brown spots are dead and dying cells.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures, wherein like elements are numbered alike throughout, the present invention relates to devices and methods that use sub-atmospheric (or negative) pressure for treating damaged central nervous system tissue. As used herein “damaged” tissue is defined to include tissue that is injured, compromised, or in any other way impaired, such as damage due to trauma, disease, infection, surgical complication, or other pathologic process, for example. Referring specifically to FIG. 1, an exemplary configuration of a sub-atmospheric central nervous system treatment device 100 of the present invention is illustrated. The sub-atmospheric central nervous system treatment device 100 may comprise a porous material 10 disposed proximate the damaged central nervous system tissue, such as brain tissue 9 for example, for delivering and distributing sub-atmospheric pressure to the damaged brain tissue 9. The sub-atmospheric central nervous system treatment device 100 may further include a vacuum source 30 in gaseous communication with the porous material 10 via a tube 20 to provide sub-atmospheric pressure to the damaged brain tissue 9.

Turning to FIG. 1 in greater detail, an exemplary configuration of a sub-atmospheric central nervous system treatment device 100 of the present invention is illustrated in situ in an animal with surrounding tissues shown in partial cross-section. The tissues illustrated include the skin 2, muscle tissue 4, skull bone 5, and the damaged brain tissue 9, above which a portion of the skull bone 5 is missing to provide treatment access to the damaged brain tissue 9. The porous material 10 may be placed in the space proximate the brain tissue 9 to provide sub-atmospheric pressure treatment to the damaged brain tissue 9. The treatment may include reducing intracranial pressure, decreasing edema, removing harmful fluids or undesirable compounds, and so forth, for example.

The porous material 10 may have pores large enough to allow undesirable compounds to be removed from the brain tissue 9 and the surrounding space/tissue(s) and pores small enough to deter or prevent the ingrowth of brain tissue into the porous material 10. In this regard, the pore size may be large enough to permit transport of material such as cytokines, toxic substances, or other mediators away from the brain tissue 9 to reduce such materials to a clinically desirable level. For example, the pore size may be large enough to permit albumin to pass through the porous material 10. In addition, the pores may be small enough (at least where the porous material 10 contacts the brain tissue 9) to deter or prevent the growth of tissue into the porous material 10 so that the porous material 10 does not adhere to and cause damage to the brain tissue 9 when removed. For example, to minimize ingrowth and to avoid the excessive production of granulation tissue which may interfere with the physiologic function of the brain, the pore size may be smaller than the that of fibroblasts and brain cells.

The porous material 10 may be homogeneous in composition and/or morphology or may have a relatively larger pore size interior to the porous material 10 or at any location where the porous material 10 does not contact the brain tissue 9. For example, the porous material 110 may include a non-ingrowth layer 112 with a sufficiently small pore size to prevent the growth of tissue therein for placement in contact with the brain, and may have an additional layer 114 of a different material that has a relatively larger pore size (e.g., larger than that of fibroblasts and brain cells) in contact with the non-ingrowth layer 112 but not in contact with the brain, FIG. 14. For instance, the porous material 10 may have a pore size sufficiently large to promote the formation of granulation tissue at other tissues in the spaces surrounding the damaged brain tissue 9. Additionally, the porous material 10 may include one or more sides or surfaces of the porous material 10 which are sealed to prevent the transmission of sub-atmospheric pressure therethrough, while at the same time having at least one surface through which sub-atmospheric pressure may be transmitted. Such a configuration of the porous material 10 can provide preferential treatment of tissue on one side of the porous material 10 while not treating tissues at the sealed sides. For instance, such a porous material 10 may be used when it is placed on brain parenchyma at its interface with the ventricular space. The parenchyma could be treated with through a surface on one side of the porous material 10; at the same time the sealed surface(s) of the porous material 10 would not drain the ventricular space so the fluid in the ventricular space would not be removed. Similarly, a porous material 10 that varies in its permeability along its length would allow sub-atmospheric pressure to be applied to the brain parenchyma while not promoting subatmospheric pressure in the cerebrospinal fluid (CSF) spaces such as the sulci, the ventricles, and the subarachnoid space and, therefore, not preferentially remove CSF from those spaces.

The porous material 10 may comprise a material is bioabsorbable or degrades harmlessly over time, such as collagen, or a material that needs to be removed after sub-atmospheric therapy is given. The porous material 10 may be one that readily conforms to the surface of brain or cavity walls easily without excessive packing and may do so without excessive trimming and shaping. For example, the porous material 10 may be provided in the form of a ribbon, or string that could be placed on or in the brain/cranium. The ribbon or string may have adequate strength so that it may be pulled out of the head without breaking or leaving residue. For instance, a ribbon or string of porous material 10 may be gradually and progressively removed as the cavity into which it is placed fills in. Thus, the porous material 10 may be in the form of a ribbon or tape or string (e.g., 5×5×200 mm) with enough resilience such that it can be pulled out thought a small hole in the skull 5 after treatment without need for second surgery. The porous material 10 may be a flexible sheet which can be folded and modified to fit in specific areas of the central nervous system such as directly in the brain parenchyma or the ventricular system following trauma.

In addition, the porous material 10 may be sufficiently compliant that so it does not press against the damaged brain to a degree that interferes with brain function. Yet, the porous material 10 may be sufficiently firm so that the porous material 10 does not collapse so much as to pull or distort the brain to a degree that might interfere with brain function. Exemplary materials that may be used in the porous material 10 may include an open-cell collagen material, polyglycolic and/or polylactic acid material, a synthetic polymer, a flexible sheet-like mesh, an open-cell polymer foam, a foam section, a porous sheet, a polyvinyl alcohol foam, a polyethylene and/or polyester material, elastin, hyaluronic acid, alginates, polydiolcitrates, polyhyrdoxybutyrate, polyhyrdoxyfumarate, polytrimethylene-carbonate, polyglycerolsebecate, aliphatic/aromatic polyanhydride, or other suitable materials, and combinations of the foregoing any of which may be fabricated by electrospinning, casting, or printing, for example. Such materials include a solution of chitosan (1.33% weight/volume in 2% acetic acid, 20 ml total volume) which may be poured into an appropriately sized mold. The solution is then frozen for 2 hours at −70° C., and then transferred to the lyophylizer with a vacuum applied for 24 hours. The material may be cross-linked by 2.5%-5% glutaraldehyde vapor for 12-24 hours (or by ultraviolet radiation for 8 hours) to provide a cast porous material 10.

Additionally, the porous material 10 may be made by casting polycapro-lactone (PCL). Polycaprolactone may be mixed with sodium chloride (1 part caprolactone to 10 parts sodium chloride) and placed in a sufficient volume of chloroform to dissolve the components. For example, 8 ml of the solution may be poured into an appropriately sized and shaped contained and allowed to dry for twelve hours. The sodium chloride may then be leached out in water for 24 hours.

It is also possible to use electrospun materials for the porous material 10. One exemplary of a formulation and method for making an electrospun porous material 10 was made using a combination of collagen Type I:chondroitin-6-sulfate (CS): poly 1,8-octanediol citrate (POC) in a ratio of 76%:4%:20%: by weight. Two solvents were utilized for the collagen/CS/POC. The CS was dissolved in water and the collagen and POC were dissolved in 2,2,2-trifluoroethanol (TFE). A 20% water/80% TFE solution (volume/volume) solution was then used. For electrospinning, the solution containing the collagen:CS:POC mixture was placed in a 3 ml syringe fitted to an 18 Ga needle. A syringe pump (New Era Pump Systems, Wantaugh, N.Y.) was used to feed the solution into the needle tip at a rate of 2.0 ml/hr. A voltage of 10-20 kV was provided by a high voltage power supply (HV Power Supply, Gamma High Voltage Research, Ormond Beach. FL) and was applied between the needle (anode) and the grounded collector (cathode) with a distance of 15-25 cm. The material was then cross-linked with glutaraldehyde (Grade II, 25% solution) and heat polymerized (80° C.) for 48 hours. It is also possible to electrospin collagen Type I porous materials 10 starting with an initial concentration of 80 mg/ml of collagen in 1,1,1,3,3,3-hexafluoro-2-propanol (HFP), then use the same electrospinning conditions as the collagen:CS:POC combination.

An additional method for creating porous materials 10 is to use thermal inkjet printing technologies. Bioabsorbable materials such as collagen, elastic, hyaluronic acid, alginates, and polylactic/polyglycolic acid co-polymers may be printed. As examples, Type I collagen (Elastin Products Co., Owensville, Mo.) dissolved in 0.05% acetic acid, then diluted to 1 mg/ml in water can be printed, as can sodium alginate (Dharma Trading Co., San Raphael, Calif.) 1 mg/ml in water. A mixture of Type I collagen (2.86 mg/ml in 0.05% acetic acid) and polylactic/polyglycolic acid (PURAC America, Blair, Nebr.) (14.29 mg/ml in tetraglycol (Sigma Aldrich, St. Louis Mo.)) can also be printed. Hardware from a Hewlett Packard 660c printer, including the stepper motors and carriage for the cartridges, can be mounted to a platform. The height of the hardware above the platform can then be adjusted for printing in layers. The porous material 10 may comprise an MRI-compatible material so an MRI can be performed while the porous material 10 is in place.

Turning next to the delivery of sub-atmospheric pressure to the porous material 10 and distribution to the damaged brain tissue 9, a tube 20 may be connected directly or indirectly in gaseous communication with the porous material 10 at the distal end 22 of the tube 20. For example, the distal end 22 of the tube 20 may be embedded in the porous material 10 or may be placed over the porous material 10. The distal end 22 of the tube 20 may also include one or more fenestrations to assist in delivering the sub-atmospheric pressure to the porous material 10 and the damaged brain tissue 9. The tube 20 may extend through an opening in the skin and subcutaneous tissue 2 which may be secured about the tube 20 with a suture to assist in providing a seal about the tube 20. The proximal end 24 of the tube 20 may be operably connected to a vacuum source 30, such as a vacuum pump, to provide sub-atmospheric pressure that is transmitted via the tube 20 to the porous material 10 and the damaged brain tissue 9.

The vacuum source 30 may include a controller 32 to regulate the production of sub-atmospheric pressure. For instance, the vacuum source 30 may be configured to produce sub-atmospheric pressure continuously or intermittently; e.g. the vacuum source 30 may cycle on and off to provide alternating periods of production and non-production of sub-atmospheric pressure. The duty cycle between production and non-production may be between 1 to 10 (on/off) and 10 to 1 (on/off). In addition, intermittent sub-atmospheric pressure may be applied by a periodic or cyclical waveform, such as a sine wave. The vacuum source 30 may be cycled after initial treatment to mimic a more physiologic state, such as several times per minute. The sub-atmospheric pressure may be cycled on-off as-needed as determined by monitoring of the pressure in the damaged brain tissue 9. In general, the vacuum source 30 may be configured to deliver sub-atmospheric pressure between atmospheric pressure and 75 mm Hg below atmospheric pressure (such as ˜20 mm Hg, for example) to minimize the chance that the sub-atmospheric pressure may be deleterious to the brain parenchyma. (Excessive negative pressure may result in bleeding into the parenchyma). The application of such a sub-atmospheric pressure can operate to remove edema from the damaged brain tissue 9, thus preserving neurologic function to increase the probability of recovery and survival in a more physiologically preserved state. In addition, the application of sub-atmospheric pressure can normalize intracranial pressure to a clinically desirable level, normalize tissue volume and density to a clinically desirable level, and/or normalize at least one of blood pressure and heart rate to a clinically desirable level. For example, the application of sub-atmospheric pressure can normalize intracranial pressure to a substantially normal, pre-damage physiological state, normalize tissue volume and density to a substantially normal, pre-damage physiological state, and/or normalize at least one of blood pressure and heart rate to a substantially normal, pre-damage physiological state.

To assist in maintaining the sub-atmospheric pressure at the damaged brain tissue 9, a flexible cover/sheet 50 or rigid (or semi-rigid) cover may be provided proximate the damaged brain tissue 9 to provide a region about the damaged brain tissue 9 where sub-atmospheric pressure may be maintained. Specifically, with reference to FIGS. 1, 11, 13, a cover 50 may be provided over the damaged brain tissue 9 and porous material 10 by adhering the cover 50 to tissues such as skin 2, 202, 502 proximate the damaged brain tissue 9 to define an enclosed region about the damaged brain tissue 9 and porous material 10. For instance, the cover 50 may be glued to the skin 2, 202, 502 and/or other appropriate tissues using an adhesive, such as a fibrin glue. The adhesive may comprise an auto-polymerizing glue and/or may desirably include a filler to provide the adhesive with sufficient bulk to permit the adhesive to conform to the shapes of the potentially irregular surfaces which the adhesive contacts. The adhesive may be provided as a separate component or as a portion of the cover 50 to provide a self-adhesive cover 50. For instance, the cover 50 may comprise a flexible self-adhesive sheet which includes a suitable adhesive on one or more of its surfaces.

Sub-atmospheric pressure may be delivered under the cover 50 by cooperation between the cover 50 and the tube 20. Specifically, the cover 50 may include a vacuum port to which the distal end 22 of the tube 20 connects to provide gaseous communication between the tube 20 and the space under the cover 40 over the damaged brain tissue 9. Alternatively, the cover 50 may include a pass-through 52 through which the tube 20 passes so that the distal end 22 of the tube 20 is disposed interior to, and in gaseous communication with, the space under the cover 50 over the damaged brain tissue 9, FIG. 1. In addition the cover 50 may further protect the damaged brain tissue 9 from exogenous infection and contamination beyond the protection already afforded by the porous material 10 and sutured skin 2. Likewise, the cover 50 may further protect surrounding tissues from the spread of infection from the damaged brain tissue 9 such as brain abscesses, meningitis, and spinal tissue infection. As an alternative, a cover 50 need not be used and the skin 2 and/or dura may sutured, stapled, or clipped closed to provide a region about the damaged brain tissue 9 at which sub-atmospheric pressure may be provided.

In another of its aspects, the present invention also provides a method for treating damaged brain tissue using sub-atmospheric pressure. In particular, the method may comprise locating a porous material 10 proximate the damaged brain tissue 9 to provide gaseous communication between one or more pores of the porous material 10 and the damaged brain tissue 9. The porous material 10 may be sealed in situ proximate the damaged brain tissue 9 to provide a region about the damaged brain tissue 9 for maintaining sub-atmospheric pressure at the damaged brain tissue 9. A tube 20 may be connected to the porous material 10 at a distal end 22 of the tube 20, and the porous material 10 may be sealed in situ by sutures 7 in the skin 2 and subcutaneous tissues to provide a region about the damaged brain tissue 9 for maintaining sub-atmospheric pressure. A further airtight dressing or cover 50 may optionally be placed over the suture site to promote an airtight seal. The method may also include the step of adhesively sealing and adhering the cover 50 to tissue, e.g., skin 2, surrounding the damaged brain tissue 9. The cover 50 may be provided in the form of a self-adhesive sheet 50 which may be located over the damaged brain tissue 9. In such a case, the step of sealing the cover 50 may include adhesively sealing and adhering the self-adhesive sheet 50 to tissue surrounding the damaged brain tissue 9 to form a seal between the sheet 50 and tissue surrounding the damaged brain tissue 9. In addition, the step of operably connecting a vacuum system 30 in gaseous communication with the porous material 10 may comprise connecting the vacuum system 30 with the vacuum port of the cover 40.

The proximal end 24 of the tube 20 may be attached to a vacuum source 30 to supply sub-atmospheric pressure to the damaged brain tissue 9 upon activation of the vacuum system 30. For example, the sub-atmospheric pressure may be maintained at about 20 to 75 mm Hg below atmospheric pressure. The sub-atmospheric pressure may be maintained at the damaged brain tissue 9 for a time sufficient to: 1) normalize intracranial pressure to a substantially normal, pre-damage physiological state; 2) normalize tissue volume and density to a substantially normal, pre-damage physiological state; 3) normalize at least one of blood pressure and heart rate to a substantially normal, pre-damage physiological state; 4) decrease cytokines, toxic substances, or other mediators to a clinically desirable level; and/or 5) improve cognition, consciousness, motor or sensory function of the patient, which may be indicated by the Glasgow score. In addition, the sub-atmospheric pressure may be maintained at the damaged brain tissue 9 for a time sufficient to prepare the brain tissue 9 to achieve a stage of healing and diminution of bacterial counts such that acceptance of secondary treatments (e.g., flaps) can be successful.

The method may be used for at least three hours, or can be used for many days. At the end of the vacuum treatment, the sutures 7 may be removed and the skin 2 re-opened. The porous material 10 may then be removed and the skin 2 is re-sutured closed.

EXAMPLES

Rat Brain Injuries and Sub-atmospheric Pressure Exposure

Experiment 1

An experiment was conducted to develop a model of brain contusion and vacuum treatment of the contused brain. Twelve (12) 300 gram Sprague Dawley rats were procured and allowed to acclimated to the housing conditions. For two of the animals, a MRI scan (Bruker Biospin Horizontal Bore 7 Tesla small animal scanner, Ettlingen, Germany) of the brain was obtained before any other procedures were performed. The animals were sedated with isoflurane (2% inhalation) and the scan of the brain obtained. The animals were allowed to recover from anesthesia and returned to their cages. For creation of the injury, on the day of surgery the animals were sedated with isoflurane (2-2.5% inhalation). The top of the head was shaved and the hair removed with a depilatory agent. A midline incision 1 was made down to the bone 5, FIG. 1. The right side of the skull was removed exposing the right half of the brain; the dura was left intact. The animal was placed into the stereotaxic holder on the impactor device (Pneumatic (Cortical) Impact Device; AmScien Instruments, Richmond Va.). The right forebrain of each animal was then impacted. For the first animal, a 3 mm diameter rod was impacted to a depth of 2.0 mm (Table 1, rat no. 1). This injury was not deemed to be significant enough. An attempt was made in animal 2 to increase the severity of the injury. The second animal had a 6 mm diameter rod impacted to a depth of 2.5 mm into the brain. (Table 1, rat no. 2). This injury was deemed to be too severe. For the remaining animals, a 6 mm diameter rod was impacted to a depth of 2.0 mm into the right forebrain. (Table 1, rat nos. 3-12). For the two animals in which a MRI scan had been performed prior to surgery, both animals died within 5 minutes post impaction. (Table 1, rat nos. 3 and 8.).

Two non-treatment, control animals were successfully impacted and allowed to recover from anesthesia in heated cages. (Table 1, rat nos. 4 and 5). Eight hours later the animals were re-anesthetized and a MRI scan was obtained to visualize the degree of swelling and presence of water (T2 weighted MRI image). Two vacuum treatment animals were then successfully impacted and a small piece of polyvinyl alcohol vacuum dressing (VersaFoam, Kinetic Concepts, Inc., San Antonio, Tex.) the size of the removed bone was placed over the brain. (Table 1, rat nos. 6 and 7). A small bore evacuation tube was placed on top of the dressing and below the skin. The end of the tube was cut at an angle and positioned so that the opening at the end of the tube abutted against the dressing. A side port was also cut into the side of the evacuation tube positioned so that the port was in contact with the foam dressing. The tube exited the incision site and the incision was sutured closed. A piece of thin film dressing (Ioban, 3M, St. Paul, Minn.) was placed over the incision to ensure an airtight seal. The animals were allowed to recover from anesthesia and placed into heated cages. The small bore evacuation tube was connected with a vacuum source. A low level vacuum, 25 mm Hg, i.e. 25 mm Hg below atmospheric pressure, was applied to the injured area for 8 hours for these two animals. The animals were then re-anesthetized with isoflurane (2% inhalation) and a MRI scan was performed. For one animal, the injured site was compressed when placing the animal into the MRI scanner, inducing an additional but un-quantified injury to the brain. (Table 1, rat no. 6). The scan of this animal showed that brain tissue was extruded around one edge of the vacuum dressing.

Two additional control animals were successfully impacted and a piece of the polyvinyl alcohol vacuum dressing was placed over the removed bone. (Table 1, rat nos. 9 and 12). The vacuum dressing was larger in area than that of the removed bone, and extended slightly (1-2 mm) outside the periphery of the hole that was created to expose the brain. The skin was then sutured closed and the animals were allowed to recover from anesthesia in heated cages. The animals were then re-anesthetized 24 hours later and a MRI scan was obtained. Two additional vacuum treatment animals were successfully impacted, and a larger vacuum dressing, which extended slightly (1-2 mm) outside the periphery of the hole that was created to expose the brain, was placed. A small bore evacuation tube exited the incision site and the incision was sutured closed. The evacuation tube exited the incision site parallel to the uninjured skin in the direction of the tail. A suture 7 was placed in the skin 2 of the neck and the evacuation tube 20 was secured to the skin 2 by this suture 7 to prevent the evacuation tube 20 from being displaced while the animal was ambulating. (Table 1, rat nos. 10 and 11). A small piece of the thin film dressing 50 was again placed to ensure an airtight seal. Low level vacuum, 25 mm Hg, was applied for 24 hours. The animals were then re-anesthetized and a MRI scan was obtained. At this time it was discovered that the evacuation tubing for one of these animals was blocked by a blood clot, and it was not discernible whether the vacuum was actually applied to the injured area. (Table 1, rat no. 11). FIGS. 2-8 illustrate MRI images of the rats as indicated in column 5 of Table 1, and FIGS. 10-13 schematically illustrate in partial cross-section of a selected slice from the MRI images, where reference numerals ending in “2” (i.e., 102, 202, 302, 502) refer to skin, numerals ending in “3” (e.g., 203) refer to an air pocket, numerals ending in “4” refer to muscle, numerals ending in “5” refer to skull bone, numerals ending in “6” refer to the brain, numerals ending in “8” refer to blood or other liquid, and numerals ending in “9” refer to the area of brain impaction. FIG. 9 schematically illustrates in partial cross-section the same view as FIGS. 10-13 using the same numbering conventions (i.e., skin 402, muscle 404, skull bone 405, brain 406), but in an animal prior to undergoing any of the procedures used in these experiments.

The results of the animal study showed that the control animals exhibited significant swelling with excess water in the injured tissue 109, 309 at both 8 and 24 hours post impaction. (Table 1, rat nos. 4, 5, 9, and 12, FIGS. 2, 10, 3, 5, 12, 8). The vacuum treated animals showed much less swelling and much less excess water in the injured area 209, 509 at both 8 and 24 hours post impaction (8 hours and 24 hours of vacuum treatment). (Table 1, rat nos. 7 and 10, FIGS. 4, 11, 6, 13. Also rat no. 9, FIG. 15A, versus rat 10, FIG. 15B). Based on these results it was concluded that impaction of rat brain with 6 mm diameter rod to a depth of 2.0 mm produced a significant degree of swelling post impaction which was more significant at 24 hours than 8 hours. Application of 25 mm Hg vacuum to the brain dramatically reduced swelling of the brain, particularly dramatic at 24 hours post impaction with 24 hours vacuum application.

TABLE 1 Rod diam- Fig- Rat eter Depth ure Compli- No. (mm) (mm) Group No. cations MRI* 1 3 2.0 Control None None 2 6 2.5 Control None 8 hours post- impaction 3 6 2.0 Died within 5 Pre- minutes post impaction impaction 4 6 2.0 Control 2, 10 None 8 hours post- impaction 5 6 2.0 Control 3 None 8 hours post- impaction 6 6 2.0 Vacuum - Bleeding - 8 Small compression on hours post- sponge injured site impaction when inserted into MRI machine 7 6 2 Vacuum - 4, 11 None 8 Small hours post- sponge impaction 8 6 2.0 Died within 5 Pre- minutes post impaction impaction 9 6 2 Control - 5, 12 None 24 large hours post- sponge impaction 10 6 2.0 Vacuum - 6, 13 None 24 large hours post- sponge impaction 11 6 2.0 Vacuum - 7 Vacuum tubing 24 large occluded with hours post- sponge blood clot impaction 12 6 2 Control - 8 None 24 large hours post- sponge impaction *MRI scans are T2 weighted images in which water appears white.

Comments:

Rat 1—animal to develop model, small diameter rod (3 mm) used for impaction—not included in results.

Rat 2—animal to develop model, 6 mm diameter plunger at 2.5 mm produced large injury, decreased depth to 2 mm for rest of animals—not included in results.

Rat 3—pre-impaction MRI scan performed for comparison with post impaction scan, but animal died within minutes of impaction.

Rat 4—control animal with MRI scan 8 hours post impaction showing swelling and protrusion of brain at area of impaction.

Rat 5—control animal with MRI scan 8 hours post impaction showing swelling and protrusion of brain at area of impaction.

Rat 6—vacuum treated animal with continual bleeding until vacuum applied. Small piece of polyvinyl alcohol dressing placed into hole in skull. MRI scan 8 hours post impaction/treatment. MRI technician pressed on/compressed brain when placing animal in MRI scanner with additional trauma to brain—not included in results because of human error.

Rat 7—vacuum treated animal with small piece of polyvinyl alcohol dressing placed into hole in skull. MRI scan 8 hours post impaction/treatment.

Rat 8—pre-impaction MRI scan performed for comparison with post-impaction scan, but animal died within minutes of impaction.

Rat 9—control animal with larger diameter sponge placed over defect in skull, extending beyond edges of defect. Skin sutured over sponge. Sponge placed to determine if sponge under sutured skin would be a mechanical impediment to swelling. MRI scan 24 hours post impaction.

Rat 10—vacuum treated animal with larger diameter sponge placed over defect in skull, extending beyond edges of defect. Skin sutured over sponge. Vacuum applied immediately after impaction for 24 hours, then MRI scan.

Rat 11—vacuum treated animal with larger diameter sponge placed over defect in skull, extending beyond edges of defect. Skin sutured over sponge. Vacuum applied immediately after impaction for 24 hours, then MRI scan. Tubing was clogged with blood clot and not able to determine when tube was clogged and if vacuum was actually applied to brain. Not included in results.

Rat 12—control animal with larger diameter sponge placed over defect in skull, extending beyond edges of defect. Skin sutured over sponge. Sponge placed to determine if sponge under sutured skin would be a mechanical impediment to swelling. MRI scan 24 hours post impaction.

Experiment 2

Cell death following traumatic brain injury is biphasic, with initial death due to the trauma itself, then an ongoing death as sequella to the release of excitatory amino acids, buildup of lactate, etc. The release of excitatory amino acids (glutamate, aspartate) cause a disturbance in ion homeostasis via agonist opened channel, thus increasing energy demand and increasing lactate production. Elevated levels of glutamate have been shown to be correlated with increased levels of lactate. This increase in lactate is reflective of increased energy demand during periods of impaired supply (ischemia), and is inversely related to patient outcome. Lactate production leads to apoptotic neuronal cell death.

In this preliminary study, anesthetized rats underwent an 8 mm diameter craniectomy between the bregma and lambda, 1 mm lateral to the midline. A controlled cortical impact injury with intact dura was created using the apparatus of Example 1. The impactor tip was 6 mm in diameter and the impact depth was 2 mm. The sham group had only the craniectomy; the non-treated control was impacted; and, the treated group was impacted and had 25 mm Hg sub-atmospheric pressure applied for either 48 or 72 hours.

Twenty-four hours after brain injury, the rats were anesthetized with isoflurane and placed inside a Litz-cage volume coil (38 mm inside diameter). All MRI and MRS experiments were performed using a horizontal 7T magnet (the Bruker Biospin apparatus of Example 1). A Rapid Acquisition with Relaxation Enhancement (RARE) pulse sequence with a RARE factor of 8 was used to acquire T2-weighted images. The Repetition Time (TR) was 1500 ms, the Echo Time (TE) was 41 ms, Number of Excitations (NEX) was 1, Field of View (FOV) was 4, and matrix size was 128×128.

Point Resolved Spectroscopy Sequence (PRESS) was used with a repetition time (TR) of 2500 ms, Echo Time (TE) of 20 ms, Number of Excitations (NEX) of 256, and a cubic voxel with a side length of 4 mm Variable Power Radio frequency with Optimized Relaxation Delays (VAPOR) water suppression was used during acquisition of the metabolite spectrum.

The tissue volume and integrated density of the injured (impacted) areas were calculated from the MRI scans 24 hours post impaction, with the dorsal third ventricle used as a reference for measurements. The results are shown in Table 2, with tissue volume and integrated density of injury areas in T2 weighed MRI. The tissue volume and density for the non-treated, impacted areas of the brain were significantly larger (p<0.01) than for the sham and treated areas. The tissue volume and integrated density for the sham and treated areas were not significantly different. An additional measure of edema is water content. Table 3 shows the water content (wet weight-dry weight/wet weight %) of the brain tissues with/without 48 hours after surgery/impaction. Water content of the treated areas is significantly lower than for the non-treated animals, p<0.05.

Tissue Volume and Integrated Density

TABLE 2 Animal Volume- Density- number Volume (mm³) contralateral Density contralateral Sham 18 122.21 121.405 1143068 1151479 21 103.237 101.946 1074570 1047381 22 108.095 108.003 987301 1010355 31 90.507 90.51 904097 851562 30 100.637 100.881 903032 887497 34 111.872 111.536 1085521 1068646 49 94.021 93.423 866348 876732 Mean ± SD 104.37 ± 10.8 103.96 ± 10.67 994848 ± 984807 ± 107843 114222 Injured-no treatment 27 129.981 104.6 1320469 953856 23 126.563 94.97 1183706 595285 20 119.852 101.367 1366772 957840 16 130.564 110.152 1359632 1062747 14 115.909 85.272 1380052 819699 12 127.77 103.124 1273593 851296 9 137.219 105.834 1470416 952034 29 137.872 111.114 1450040 990626 33 132.602 95.105 1511471 801290 37 141.124 93.779 1658429 871572 40 127.162 93.535 1338592 866975 41 127.162 95.367 1365380 873275 42 138.04 103.255 1342099 841890 Mean ± SD 130.14 ± 7.3 99.80 ± 7.48 1386203 ± 879875 ± 117167 113947 Injured-treated 10 129.389 122.974 1196508 1065277 11 135.218 130.77 1393198 1207696 13 128.34 119.66 1295263 1098217 19 117.629 114.788 1246274 1079762 26 104.581 97.797 1039937 853611 28 119.836 119.221 1290085 1209136 35 116.039 111.61 1197579 986314 39 99.535 95.815 971668 881767 45 93.255 83.329 884885 767881 48 86.414 84.189 1005306 780081 Mean ± SD 113.02 ± 16.4 108.01 ± 16.64 1152070 ± 992974 ± 166219 164820 Water Content % (Animal # in Parenthesis)

TABLE 3 Sham Injured-no treatment Injured-treated 78.90 (51 right side) 83.36 (9) 80.07 (10) 79.79 (51 left side) 83.97 (14) 80.02 (52) 78.91 (53 right side) 83.72 (55) 80.20 (54) 79.06 (53 left side) Mean ± SD 79.17 ± 0.42 83.68 ± 0.31 80.10 ± 0.09

The T2-weighted MR images from axial planes illustrating the localization of MR spectral voxels are shown in FIG. 16, with the spectral voxel outlined by the white box. FIG. 17 shows an example of a Single-Voxel MR spectra obtained from either a sham animal (left), a non-treated animal (center), or a treated animal (right). The spectra show low levels of lactate for the sham animal (arrow), high levels for the non-treated animal, and low levels for the treated animal. All metabolites measured are shown in Table 4. Lactate levels in sham areas were significantly lower than in non-treated animals. Lactate levels between sham animals and treated animals were not significantly different. Lactate levels in treated animals showed a trend to be lower than in non-treated animals. The remaining metabolites which were significantly different (with p values) are identified in Table 5, where the treated animals are shown not to be significantly different than the sham.

TABLE 4 Animal Number GABA Gln Glu Ins Lac NAA Tau Cr + PCr Sham 18 6.384 11.224 21.531 13.061 0 16.224 8.553 14.286 21 5.065 9.764 18.673 10.918 5.875 11.837 8.763 13.776 22 — 8.721 12.143 10.306 — 9.238 5.174 10.112 30 — 9.962 17.449 10.612 — 10.816 5.08 11.122 31 — 9.846 15.612 10.612 — 9.864 4.835 11.633 34 4.67 9.798 17.55 10.612 — 11.122 7.416 12.551 49 8.581 9.938 21.939 14.184 1.939 15.816 8.105 14.184 47 4.69 6.691 17.755 11.122 0.516 11.838 5.817 12.449 Mean ± SD 5.88 ± 1.67 9.49 ± 1.32 17.83 ± 3.13 11.42 ± 1.41 2.08 ± 2.66 12.09 ± 2.58 6.72 ± 1.66 12.51 ± 1.51 Injured - non-treated 14 — 5.712 11.122 6.042 8.481 6.498 2.885 9.686 16 — 7.244 12.653 7.699 5.49 8.828 7.909 11.735 27 — 7.401 10.034 7.984 — 6.094 4.416 8.159 29 — 10.918 14.082 9.408 4.997 7.879 7.26 10.408 20 3.515 10.408 12.041 9.467 — 8.264 5.933 10.019 23 2.654 9.405 11.224 7.18 8.702 6.811 5.359 8.686 33 — 9.551 12.857 10.408 6.916 8.354 8.832 11.633 37 — 7.053 13.776 7.673 10.306 8.714 7.45 10.51 40 6.426 10.188 17.755 11.531 6.761 12.653 8.866 13.571 41 4.58 7.846 13.878 9.179 3.193 9.727 6.208 10.141 42 — 9.17 15.816 11.112 10.204 10.51 8.925 13.163 Mean ± SD 4.84 ± 1.47 8.63 ± 1.66 13.20 ± 2.22  8.89 ± 1.74 7.23 ± 2.41  8.58 ± 1.89 6.73 ± 1.97 10.70 ± 1.69 Injured - treated 13 — 4.863 12.143 8.045 2.848 7.989 5.753 10.155 15 4.635 9.331 16.837 9.862 6.743 10.51 8.244 11.939 17 5.198 10.918 18.163 12.959 2.859 12.959 10.061 15.408 26 6.481 9.124 18.367 11.735 — 11.327 7.186 11.735 28 3.615 8.346 10.714 8.404 — 6.425 5.859 9.199 19 4.266 8.612 14.082 10.816 — 9.328 8.201 11.837 35 5.976 9.278 14.184 11.633 5.961 12.245 8.263 13.163 36 4.743 9.458 14.694 10.063 8.833 9.594 8.42 11.429 39 5.447 8.855 15.714 12.245 2.687 11.531 8.563 12.755 45 5.809 10.204 21.429 16.224 2.394 14.796 9.993 15.204 48 4.271 9.515 20. 12.041 2.542 12.041 8.13 13.571 Mean ± SD 5.04 ± 0.89 8.95 ± 1.53 16.03 ± 3.29 11.28 ± 2.27 4.36 ± 2.47 10.79 ± 2.36 8.06 ± 1.38 12.39 ± 1.90

TABLE 5 Groups Glu Inos NAA Total Cr Non-treat vs sham 0.002 0.006 0.002 0.029 Non-treat vs treat 0.030 0.007 0.03 0.033 Sham vs treat 0.191 0.862 0.228 0.888

Nitrotyrosine is a marker for cell degradation and death. Analysis for neuronal degradation and death was accomplished by immunohistochemical staining for nitrotyrosine on brain samples harvested 72 hours after surgery/impaction. The treated animals were exposed to sub-atmospheric pressure for the entire 72 hours. FIG. 18A shows histological sections of a non-treated brain section, and FIG. 18B shows a treated brain section. The black dots represent cells that are undergoing degradation and death. There are many more degrading and dying cells in the non-treated section than in the treated section, showing the benefit of treatment.

These and other advantages of the present invention will be apparent to those skilled in the art from the foregoing specification. Accordingly, it will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It should therefore be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention as set forth in the claims. 

What is claimed is:
 1. An apparatus for administering sub-atmospheric pressure to damaged central nervous system tissue comprising: a. a porous electrospun bioabsorbable material for placement proximate the damaged central nervous system tissue, the porous electrospun bioabsorbable material having a pore structure configured to communicate sub-atmospheric pressure therethrough for transmission to the damaged central nervous system tissue, and having a selected surface for placement proximate the damaged central nervous system tissue configured to prevent the growth of central nervous system tissue into the porous electrospun bioabsorbable material; and b. a cover for enclosing the damaged central nervous system tissue and the electrospun bioabsorbable material, the cover configured to maintain sub-atmospheric pressure at the electrospun bioabsorbable material and damaged central nervous system tissue.
 2. The apparatus according to claim 1, comprising a source of sub-atmospheric pressure in gaseous communication with the porous material for distributing the sub-atmospheric pressure to the central nervous system tissue to be treated.
 3. The apparatus according to claim 1, wherein the bioabsorbable material comprises a granulating surface configured to promote the formation of granulation tissue thereat.
 4. The apparatus according to claim 1, wherein the cover comprises a self-adhesive sheet.
 5. An apparatus for administering sub-atmospheric pressure to damaged central nervous system tissue comprising: a. a porous cast bioabsorbable material for placement proximate the damaged central nervous system tissue and having a pore structure configured to communicate sub-atmospheric pressure therethrough for transmission to the damaged central nervous system tissue, and having a selected surface for placement proximate the damaged central nervous system tissue configured to prevent the growth of central nervous system tissue into the porous cast bioabsorbable material; and b. a cover for enclosing the damaged central nervous system tissue and the cast bioabsorbable material, the cover configured to maintain sub-atmospheric pressure at the cast bioabsorbable material and damaged central nervous system tissue.
 6. The apparatus according to claim 5, comprising a source of sub-atmospheric pressure in gaseous communication with the porous material for distributing the sub-atmospheric pressure to the central nervous system tissue to be treated.
 7. The apparatus according to claim 5, wherein the bioabsorbable material comprises a granulating surface configured to promote the formation of granulation tissue thereat.
 8. The apparatus according to claims 5, wherein the cover comprises a self-adhesive sheet.
 9. An apparatus for administering sub-atmospheric pressure to damaged central nervous system tissue comprising: a. a porous printed bioabsorbable material for placement proximate the damaged central nervous system tissue and having a pore structure configured to communicate sub-atmospheric pressure therethrough for transmission to the damaged central nervous system tissue, and having a selected surface for placement proximate the damaged central nervous system tissue configured to prevent the growth of central nervous system tissue into the porous printed bioabsorbable material; and b. a cover for enclosing the damaged central nervous system tissue and the printed bioabsorbable material, the cover configured to maintain sub-atmospheric pressure at the printed bioabsorbable material and damaged central nervous system tissue.
 10. The apparatus according to claim 9, comprising a source of sub-atmospheric pressure in gaseous communication with the porous material for distributing the sub-atmospheric pressure to the central nervous system tissue to be treated.
 11. The apparatus according to claim 9, wherein the bioabsorbable material comprises a granulating surface configured to promote the formation of granulation tissue thereat.
 12. The apparatus according to claim 9, wherein the cover comprises a self-adhesive sheet.
 13. The apparatus according to any one of claims 1-3, 4-7, 8-11, and 12, wherein the bioabsorbable material comprises a porous open-cell material.
 14. The apparatus according to claim 13, wherein the open-cell material comprises collagen.
 15. The apparatus according to any one of claim 1, 5, or 9, wherein the bioabsorbable material comprises polydiolcitrate, polyglycolic acid, polylactic acid, elastin, hyaluronic acid, chitosan, alginates, polyvinyl alcohol, polyethylene, polyester, polyhydroxybutyrate, polyhydroxyfumarate, polytrimethylene-carbonate, polyglycerolsebecate, aliphatic polyanhydride, aromatic polyanhydride, polycaprolactone, or combinations thereof.
 16. The apparatus according to any one of claim 1, 5, or 9, wherein the bioabsorbable material comprises a ribbon or string of porous material.
 17. The apparatus according to any one of claim 1, 5, or 9, wherein the bioabsorbable material comprises one or more of a synthetic polymer, a flexible sheet, and a porous sheet.
 18. The apparatus according to any one of claim 1, 5, or 9, wherein the bioabsorbable material comprises a sealed surface that is sealed to prevent the transmission of sub-atmospheric pressure therethrough.
 19. The apparatus according to any one of claims 1, 5 and 9, wherein the pore structure comprises a pore size smaller than the size of fibroblasts and central nervous system cells.
 20. The apparatus according to any one of claims 1, 5 and 9, wherein the pore structure comprises a pore size of the open-cell material that is larger than that of fibroblasts.
 21. The apparatus according to any one of claims 1, 5 and 9, wherein the pore structure comprises a pore size large enough to allow movement of proteins the size of albumin therethrough.
 22. The apparatus according to any one of claims 1, 5 and 9, wherein the pore structure comprises a pore size gradient, wherein pore size varies along a selected direction through the bioabsorbable material.
 23. The apparatus according to any one of claims 2, 6 and 10, wherein the source of sub-atmospheric pressure comprises a vacuum pump.
 24. The apparatus according to any one of claims 2, 6 and 10, wherein the source of sub-atmospheric pressure is configured to supply a sub-atmospheric pressure of about 25 mm Hg.
 25. The apparatus according to any one of claims 2, 6 and 10, wherein the source of sub-atmospheric pressure is configured to supply a sub-atmospheric of up to about 75 mm Hg. 